In recent years, lighting apparatuses that use light emitting diodes (LEDs) have become widely used in a variety of fields since they have a property whereby it is possible to easily realize a panel-type lighting apparatus with low power consumption and a long lifespan. The LEDs used in such lighting apparatuses are a panel-type light emitting device where light is emitted from the surface of a semiconductor substrate and it is known that the radiation pattern of such light (hereinafter also referred to as the “light distribution pattern”) has an intensity distribution that is proportional to cos θ (i.e., according to Lambert's cosine law) and can be approximated to a Lambertian surface. Here, θ is the angle made by light beams relative to a normal (the optical axis) to the light emitting surface.
Since the light distribution pattern of the light radiated from a panel-type light emitting device has Lambertian characteristics, the luminous intensity radiated in a direction inclined by 60° from the optical axis that is perpendicular to the light emitting surface will be around 50% of the luminous intensity radiated toward the optical axis, and therefore it can be understood that the light radiated from an LED light source has an extremely wide distribution on a hemispherical plane.
Although such wide-angle light distribution characteristics are favorable for applications such as a ceiling light that is a type of light fitting attached to the ceiling, for applications such as a projector light source, a spotlight and a display apparatus, light is radiated as far as unnecessary regions, and as a result there is the problem that the radiated intensity in the region where light is fundamentally necessary is insufficient.
To solve such problem, an existing LED apparatus is normally constructed by mounting an LED chip in a cup part of a lead mount, covering the LED chip and part of the lead mount with a sealing member made of a transparent resin, and forming a peak portion of such sealing member in a bullet shape to achieve the function of a convex lens. By using such construction, the diffusion of light radiated from the LED chip is controlled (see Patent Literature 1, for example).
An example of a display apparatus constructed by laying out a plurality of LED devices with bullet-shaped resin sealing constructions in two dimensions has also been disclosed (see Patent Literature 2, for example). However, when fabricating such display apparatuses, it takes a lot of work to successively mount a plurality of LED devices on a substrate. Also, since the dimensions of LED devices are as large as around several mm, it is not possible to construct a high-resolution display apparatus that has a narrow pitch. For this reason, the LED display disclosed in Patent Literature 2 and LED display apparatuses of such type are limited to applications in the field of giant display apparatuses which in practice will be set up outdoors.
To solve such practical issues, a technology that applies semiconductor processing technology to manufacture a microlens array (an array of on-chip lenses), which resembles the sealing members of bullet-shaped LED devices, on an array of light sources provided on the same substrate has been disclosed (see Patent Literature 3). By using such technology, it has become possible not only to form a lens array in a single operation but also to drastically reduce the disposing interval of lenses, which was previously limited to around several millimeters, to a level of several tens of micrometers. By doing so, this opens up the potential of display apparatuses that have the same high resolution as liquid crystal display apparatuses that have been widely commercialized but also has higher luminance than liquid crystal display apparatuses.